Updated: 2/15/2020

Legionella pneumophila

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Snapshot
  • A 60-year-old man is brought to the emergency department for confusion, cough, and diarrhea. He had recently attended a conference and stayed at an old hotel where other people reported similar symptoms. His past medical history includes chronic obstructive pulmonary disease and hypertension. He smokes 1 pack per day. On physical exam, his oxygen saturation is 92% on room air. There are fine crackles bilaterally on chest auscultation. A chest radiograph reveals diffuse patchy infiltrates. He is also found to have hyponatremia. A urine antigen test was sent for definitive diagnosis.
Introduction
  • Classification
    • Legionella pneumophila
      • an aerobic, facultative, intracellular gram - rod
    • transmission
      • aspiration of contaminated water/soil
        • air conditioning
        • hot tubs
        • swimming pools
  • Epidemiology
    • demographics
      • more common in the elderly
    • risk factors
      • cruise ships
      • smoking
      • immunosuppression
      • hospitalization
  • Pathogenesis
    • organism is phagocytosed into alveolar macrophages, where they replicate
    • bacterial spread occurs when they escape from macrophage vacuoles leading to host cell osmotic lysis
  • Associated conditions
    • Legionnaires disease (most common)
      • lobar or insterstitial pneumonia
      • gastrointestinal and central nervous system involvement
      • more common in smokers and those with chronic lung diseases
    • Pontiac fever
      • mild and flu-like without significant pulmonary involvement
  • Prognosis
    • Pontiac fever is self-limited
Presentation
  • Symptoms
    • Legionnaires disease
      • cough with sputum production
      • gastrointestinal symptoms
        • nausea or vomiting
        • water diarrhea
      • central nervous system symptoms
        • confusion
        • encephalopathy
    • Pontiac fever
      • malaise
      • headache
      • malaise
  • Physical exam
    • fever
    • Legionnaires disease
      • altered mental status
      • dyspnea
      • relative bradycardia
      • pneumonia
Imaging
  • Chest radiography
    • indication
      • all patients
    • findings
      • lobar consolidation or
      • diffuse patchy infiltrates
Studies
  • Labs
    • urine antigen test
      • diagnostic
    • does not Gram stain well, so it requires a silver stain 
    • sputum culture
      • requires special media for culture
      • charcoal yeast extract agar buffered with iron and cysteine  
    • hyponatremia
    • transaminitis
  • Making the diagnosis
    • based on clinical presentation and laboratory studies
Differential
  • Mycoplasma pneumoniae
    • distinguishing factor
      • typically does not present with gastrointestinal or central nervous system involvement
Treatment
  • Medical
    • antibiotics
      • indication
        • all patients
      • drugs
        • macrolides
        • respiratory fluoroquinolones (levofloxacin and moxifloxacin)
Complications
  • Respiratory failure
 

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